The 18-year-old replaced Dan James in added time at the end of the game to make his first appearance for the Reds.
Fish has been an Under-23s regular this season and said this opportunity will only drive him on further.
“It's a dream come true, to be honest,” he told MUTV after the match.
“I've been at the club for 10 years now. Every day in training, you work hard and this is the reward that you get. I really enjoyed it.
"It's the sort of feeling that I've never had before. Nerves, a little bit, excitement, but when you're on the pitch it always goes away and you focus.